The present invention relates to a propagation time measurement device that transfers a signal between a base station and a terminal to measure the propagation time of the signal.
A known propagation time measurement device estimates the time of a signal propagated between a base station and a terminal (for example, refer to Japanese Laid-Open Patent Publication Nos. 9-170364, 2003-13644, 2006-512515, and 2008-515315). More specifically, the base station transmits a signal to the terminal. The terminal that receives the signal returns the signal to the base station. The propagation time measurement device uses the signal received by the base station to estimate the propagation time of the signal. The application of such a propagation time measurement device to an electronic key system has been discussed. An electronic key system verifies an electronic key through wireless communication performed between the electronic key and a vehicle. Unauthorized communication may be established between the vehicle and an electronic key by using a relay. The application of the propagation time measurement device would prevent such unauthorized verification of the electronic key.